The physical properties of polyurethane foams can vary based on variations in the components used to create the foams such as which crosslinker, catalyst, and blowing agent are used, as well as the concentrations of polyols, water, humectants, and surfactants are used in producing the foams. The type of surfactant can have an effect on the physical properties such as rigidity, density, and porosity of the foam and depends on factors such as: the emulsification property and its effect on the polyols, water, and humectants; the nucleation of the air bubbles; the stabilization of gas bubbles in the foam that don't coalesce; and the controlled cell opening. A single surfactant is rarely able to produce a foam with the desired physical properties, thus, typically a combination of surfactants are used. Traditionally, silicone surfactants have been used.
Surfactants with higher silicone contents lower the surface tension of the foams and, thus, help increase the amount of air bubbles in the foam during mixing. The foam formation includes various stages: generation of bubbles; packing of the foam network and stabilization; and final curing. In each of these stages, silicone surfactants are essential for the production of flexible, polyurethane foam systems. Without the use of a surfactant with such functionalities, the foaming system will experience major coalescence and collapse. Also, the size of cells in the foam and the air permeability of the foam is directly related to the functionality of the surfactant. Thus, surfactants having the proper functionality are requires in order to have the proper porosity, cell size, and density of the foams produced.
Recent trends have favored the use of natural oil polyols over their petroleum counterparts in the polyurethane market. However, the use of such natural oil polyols in place of their petroleum counterparts affects the resin stability of the foam which is a result of the nature of the different oil polyols being used. For instance, although soy polyols have good polarity resulting from the presence of hydroxyl groups in the molecule having a hydrophobic backbone, such properties are distinct from a petroleum polyol that is relatively non-polar and oleophilic. The difference in the polarity requires the use of a good surfactant with the soy polyols in order to keep crosslinkers such as water, glycerol, and their blends in homogenous foam in the polyol mixture to produce foam with the desired properties.
Lecithin has been used in foams as disclosed in US Patent Application US20110062370. Lecithin is a complex mixture of phospholipids and other components such as glycerol lipids. The use of standard fluid lecithin typically requires an aliphatic solvent to remain in solution. Without the use of such solvent, lecithin is typically modified or combined with other surfactants in order to improve functionality.
Polyols are integrally used in the rigid polyurethane industry. There is a growing desire to use more green or environmentally friendly products in such industry. One solution is to replace petroleum based polyols with soy based polyols. However, the replacement of petroleum based polyols with soy based polyols is problematic since polyurethane foams made with 100% soy polyol do not offer very good foam structure and rigidity due to the limited hydroxyl functionality of the soy polyols. Also, the different nature of the hydrocarbon groups in the petroleum based polyols v. the biobased polyols results in compatibility issues that need to be overcome. The addition of polar components such as glycols or glycerols to such soy polyols has shown some advantage in the resultant blends and the final properties of foams including such components depends on the types of polyol and its hydroxyl value, surfactant type and concentration, and blowing agent used. The compatibility of all of these components is a hurdle to the foam industry since it is important to get good compatibility without causing any phase separation for periods of time in order to achieve the desired physical properties.
Thus, the choice of which surfactant to use will depend on the chemical composition and processing of the polyols and other additives used to produce the foam. This diversity of foams being produced requires the use of surfactants that are not commonly used. Although short term stability can be achieved with different surfactants and their blends, getting long term stability is required to produce foam with reasonable consistency and superior functionalities. Thus, a need exists for an emulsifier system that can produce foams including natural oil polyols.
Lecithin is a polar lipid substance found in animal and plant tissues such as, for example, egg yolk and soy bean. Lecithin is composed of various constituents including, but not limited to, phospholipids, such as, for example, phosphatidyl choline (“PC”), phosphatidyl inositol (“PI”), and phosphatidyl ethanolamine (“PE”). With their unique surface active properties, lecithins can be used in a wide range of applications such as food, feed, pharmaceuticals, and a variety of industrial applications.
Further, lecithin may be used in applications where modification of the boundary layer between substances is desirable. In the presence of immiscible liquid phases, lecithin can reduce the interfacial surface tension and function as an emulsifier. When used with two or more solid phases, lecithin can function as a lubricant and/or release agent.